Geometry Glossary

radius:	In a circle, a radius is a segment from the center to any point on the circle.
radius of a regular polygon:	A radius of the regular polygon is a segment from the center to a vertex of the polygon.
ray:	XY consists of 3FY and all points P such that Y is between X and P.
rectangle:	A parallelogram with four right angles.
reflection:	In a plane, a reflection about line I is a transformation which maps each point P into a point P such that (1) if P is on 1, then P' = P, and (2) if P is not on 1, then I is the perpendicular bisector of PP'.
regular polygon:	A convex polygon that is both equilateral and equiangular.
regular polyhedron:	A polyhedron in which all the faces are congruent regular polygons.
remote interior angle:	An interior angle that is not adjacent to the given exterior angle.
rhombus:	A parallelogram with four congruent sides.
right angle:	An angle with a measure of 90.
right cylinder:	A cylinder in which a segment connecting a pair of corresponding points of the bases is perpendicular to the bases.
right prism:	A prism in which the lateral edges are perpendicular to the bases.
right triangle:	A triangle with one right angle.
rotation:	A rotation Rp,,,, of point A about point P through an angle of measure m is a transformation which maps A into its rota- tion image A' such that PA = PA' and m Z-APA' = m.
rotational symmetry:	A figure has rotational symmetry if there is a rotation in which the figure and its image coincide under the rotation.

Note: The terms in this collection may not be entirely accurate.
They are for reference only.

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